In various fields centered on the electric and electronic industries, along with seeking to sophisticate electronic devices, such as reduction in size, acquisition of multifunctionality, and speedup of communication rate, circuit substrates used in such electronic devices are required to have a further dense structure. To respond to such demands for a dense structure, multilayered circuit substrates are developed.
A multilayered circuit substrate is manufactured, for example, through forming a conductor on an electrically insulating layer that is laminated on an inner layer substrate comprising an electrically insulating layer and a conductive layer formed on the surface of the electrically insulating layer, and repeating formation of an electrically insulating layer and a conductor. To respond to demands for such multilayered circuit substrates, various thermoset resin compositions are proposed (Patent Literature 1 to 3).
Patent Literature 1 describes using a resin composition that contains a specific epoxy resin, a phenol resin, a maleimide compound, and an inorganic filler in order to solve a problem caused by a highly-filled inorganic filler.
Patent Literature 2 describes a resin composition that contains a specific epoxy resin, curing agent, and inorganic filler. This resin composition can be preferably used for formation of an insulating layer of a circuit substrate.
Paten Literature 3 describes that, in order to provide a prepreg and the like excellent in the low thermal expandability and warpage characteristics, a thermoset resin composition layer included in the prepreg is composed of a thermoset resin composition that contains a specific maleimide compound, a specific siloxane diamine, and an amine compound having a specific acidic substituent.